I'm a biochemist, and in my experience even in a laboratory
environment it requires quite a bit of care to keep a pH electrode
working properly. They are fragile and sensitive to contamination
with organic materials. What I try to do is make my solutions up by
weighing
out the buffering acid or base and its salt so I know what pH I'm
getting, rather than the traditional HCl titration. Then you can
check for crass errors with a pH paper if you want to. This makes
for more consistent buffers. I wonder if a similar aproach could
work for nutrient solutions for orchid culture. Phosphate would be
the obvious buffer salt but you'd probably need 10 millimolar which
if my mental aritmetic serves is 310 ppm of P, perhaps higher than
you'd want. I wonder if organic buffer salts such as tris have been
tested for this purpose?

Another low tech approach used in mammalian tissue culture is to add a
low concentration of a pH indicator dye to the solution so you can see
right away when it goes too acid (in that example)

Leo

NOOK wrote in message . ..
My 2 cent thoughts: again
I have used a lot of diff. brands of PH meters over the years. Of
course the lab quality ones do hold calib. the best. They are just not
....